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Monday, May 16, 2011

Change in Distribution of Cluster Flies

There appears to have been a change in the distribution of cluster flies around New Zealand. There has been a shift from the Lower North Island to the South Island as shown by the information in Table 1. The table shows enquiries to Kiwicare regarding help in getting rid of cluster flies.﻿﻿

Table 1. Cluster Fly Enquiries

The increase in the South Island is largely due to cluster flies hitting Southland in a big way. Invercargill, Southland has seen number of visits increase (24, 26, 167) over the three years.

This is an interesting switch. It has been reported previously that cluster flies seem to go through a ‘boom bust’ cycle in local areas. My suspicion would be that this is governed by both weather conditions and the availability of their earthworm food source. If they are in big numbers for one or two years in an area, they may significantly reduce worm numbers and so suffer a drop off in their own numbers the following season as a consequence.